Electronic devices, such as semiconductor chips, are usually tested with a battery of tests before they are shipped to customers. The tests check for the presence of known types of defects that may arise during manufacturing of the electronic device. The tests are usually generated by test engineers but many of them can also be generated automatically according to the design data for a particular electronic device. The tests are performed by an automatic tester that runs a test program. The tester has probes for contacting each electronic device in turn and the test program is run for each device.
A test program may include a series of parametric tests to detect shorts and opens, measure power supply current, and verify that drivers will drive a sufficient current at a specified voltage. The test program may also include a series of functional tests to ensure that the various circuits on the chip are operating as designed. The functional tests can be conducted through test patterns that are supplied by the tester or by one or more built in self-test structures fabricated on the chip itself The test program may also include performance tests to sort passing devices according to their speed. The program may also include tests of the power supply current drawn by the chip after test patterns have been applied to the chip.
In production, the test program is run to completion only on devices that pass all tests. To save test time and money, the test program is usually stopped immediately after the first failing test on a particular device, and that failing device is marked or sorted as a fail.
As experience with test fails and defects on electronic devices becomes available, the test program may be updated, adding or deleting tests or reordering tests in the program to optimize test efficiency. After the updated test program has been generated, it must then be compiled and loaded into the tester. The program must then be qualified for use on subsequent production electronic devices. That is, the test program itself must undergo an evaluation to ensure that it is properly functioning. The updating and reordering steps introduce the possibility of error into the program that could, for example, eliminate important tests and allow failing devices to pass. In addition, these steps of reviewing and analysing test data from failing devices, then using the analysis to update a test program, and then qualifying the new test program for use in production, have been time consuming and costly.
A better solution is needed that provides for rapid and low cost updating of test programs that reduces the risk of error. This solution is provided by the following invention.